1. Field of the Invention
The present invention relates to an image forming apparatus having a fixing temperature control function and an image forming system having the image forming apparatus.
2. Description of Related Art
Generally, a related art image forming apparatus employing an electrophotographic method includes a fixing unit fixing a developer image formed on a surface of an image carrier such as a photosensitive drum onto a recording medium. Such a fixing unit includes a heat roller having a heating element and a pressure roller disposed pressed against the heat roller. When the recording medium having the developer image transferred thereon passes between the heat roller and the pressure roller, the heat and pressure is applied, thereby fixing the developer image onto the recording medium.
The related art image forming apparatus having such a fixing unit usually includes a fixing temperature control function controlling fixing temperature by monitoring surface temperature of the heat roller. For example, Japanese Un-examined Patent Application Publication No. H05-46051 discloses a prior art image forming apparatus including a timer mechanism arranging a time between a time at which surface temperature of the heat roller reaches a prescribed temperature and a time at which outer circumference surface temperature of the pressure roller becomes uniformalized.
In the image forming apparatus having the fixing temperature control function described above, however, the fixing temperature to begin fixing operation is fixed so as to secure image quality of the image to be fixed onto the recording medium, and the fixing operation halts until the surface temperature of the heat roller reaches the prescribed fixing temperature. Consequently, for example, in a case of beginning printing operation immediately after the image forming apparatus is activated, the print operation does not begin until the heat roller reaches the prescribed fixing temperature, causing prolongation of a time period until completion of printing. Since the fixing temperature to begin the fixing operation is inflexible, appropriate fixing temperature corresponding to image data or the recording medium cannot be selected, causing difficulty in image quality enhancement.
The present invention provides an image forming apparatus capable of adjusting a time period until fixing temperature reaches an appropriate level to begin fixing operation according to image data or a recording medium. Moreover, the present invention provides the image forming apparatus capable of obtaining fixing stability and enhancing fixing quality by such an adjustment of the fixing temperature to the appropriate level to begin the fixing operation.